The present invention relates to improvements in form, fill and seal machines, and more particularly to a bag forming machine wherein an endless supply of plastic film with a zipper intermediate the edges is fed over a forming and filling tube and the edges sealed to form a tubular bag.
In a form, fill and seal operation, an endless continuous supply of film is brought forwardly and is shaped and wrapped around a filling and forming tube. The shaped film has its edges brought together and joined to form a tubular container. Contents are dropped through the filling tube into the container and cross-seals are formed to provide lengths of bags which are cut apart. In one method of forming bags in a form, fill operation, the film is provided with reclosable rib and groove zipper profiles extending longitudinally along the film parallel to the forming axis of the film. In the formation of the film into tubular form, the profiles can be joined as the bag is formed. It has been discovered that a stable operation can be accomplished by utilizing film where the profiles are already joined and are located intermediate the edges of the film. In this operation, the edges of the film are brought together to form a bottom seam for the bag. An example of a bag formation where the profiles are brought together is shown in Tilman U.S. Pat. No. 4,355,494. In U.S. Pat. Christoff and Ausnit 4,617,683, the formation of bags is illustrated where the raw edges of the film are joined, and in the present arrangement, a formation procedure such as that shown in the Christoff et al patent is employed with film being supplied where the interlocked profiles are located intermediate the edges of the film.
The packaging of products for retail sale and consumption has developed gradually over the years in order to enhance the ease with which the consumer can open the packaging in order to gain access thereto for use or consumption of the food product therein. In the form, fill and seal operation described above, such reclosable packages can be developed at relatively high manufacturing speed using an endless supply of film where the profiles are already extruded as part of the film and previously interlocked. In such packaging and package making, the containers are manufactured with the interlocking rib and groove profiles accurately and critically made so that they will protect the contents, such as foodstuffs, therein and yet be readily opened and reclosed. The profiles are made to be very relatively minute, and as such with accurate manufacturing tolerances, the shape and size of the profile must be accurately maintained and not distorted either in manufacture or in storage. It is a desirable attribute of such packaging that the bags be closed securely in an airtight manner to maintain freshness of a food product remaining within the package. The food products may be of varying types such as that which are packaged and stored within a box or carton which has the bag as an internal liner or pouch to contain dry cereal products. Other forms of packages or pouches can be made which are handled, stored and sold without a protective carton surrounding them.
The film from which the bag is made is normally made by an extrusion process. In the process, the interlocking profiles which will form the zipper for the bag are extruded and are very small, but are critically shaped and sized so that they will interlock with optimum strength. In the process of manufacture of the film, when it is extruded and cooled, it is continuously wound on a roll to be stored and shipped to the bag manufacturer. The film is normally folded double with the interlocking zipper profiles located intermediate the edges of the film and essentially at the doubled edge of the film.
The doubled film thus will be thicker at the location of the interlocked profiles to avoid the thicker part of the film from building up on the roll as it is wound, the film is led spirally back and forth across the axis of the roll so that the location of the zipper changes axially as layers of the film are built up on the storage roll. This means that as the film is unwound off the storage roll, the location of the zipper will shift axially along the roll as the layers are removed from the roll. The forming machine, however, requires that the film be in one fixed location as it is fed and wrapped over the forming and filling tube.
In order to positively locate the film relative to the required position of the film when it is wrapped on the tube, it has heretofore been necessary to provide a mechanism which continually moves the supply roll axially in an amount to positively locate the zipper at the same location as the film is unwound. This requires special equipment to carry the heavy roll of film and to continually move it a proper amount in the axial direction. This also requires that the film always be wound on the supply roll in a uniform manner so that a given mechanism which moves the roll axially will always position the zipper correctly.